It is well known for lubricating oils to contain a number of surface active additives (including antiwear agents, dispersants, or detergents) used to protect internal combustion engines from corrosion, wear, soot deposits and acid build up. Often, such surface active additives can have harmful effects on engine component wear (in both iron and aluminium based components), bearing corrosion or fuel economy. A common antiwear additive for engine lubricating oils is zinc dialkyldithiophosphate (ZDDP). It is believed that ZDDP antiwear additives protect the engine by forming a protective film on metal surfaces. ZDDP may also have a detrimental impact on fuel economy and efficiency and lead and copper corrosion. Consequently, engine lubricants may also contain a friction modifier to obviate the detrimental impact of ZDDP on fuel economy and corrosion inhibitors to obviate the detrimental impact of ZDDP on lead and copper corrosion. Other additives may also increase lead corrosion.
Further, engine lubricants containing phosphorus compounds and sulphur have been shown to contribute in part to particulate emissions and emissions of other pollutants. In addition, sulphur and phosphorus tend to poison the catalysts used in catalytic converters, resulting in a reduction in performance of said catalysts.
With increasing control of both the formation of sulphated ash and release of emissions (typically to reduce NOx formation, SOx formation) there is a desire towards reduced amounts of sulphur, phosphorus and sulphated ash in engine oils. Consequently, the amounts of phosphorus-containing antiwear agents such as ZDDP, overbased detergents such as calcium or magnesium sulphonates and phenates have been reduced. As a consequence, ashless additives such as esters of polyhydric alcohols or hydroxyl containing acids including glycerol monooleate and alkoxylated amines have been contemplated to provide friction performance. However there have been observations that ashless friction modifiers may in some instances increase corrosion of metal, namely, copper or lead. Copper and lead corrosion may be from bearings and other metal engine components derived from alloys using copper or lead. Consequently, there is a need to reduce the amount of corrosion caused by ashless additives. However, reducing the levels of antiwear and other ash-containing additives may result in increasing amounts of wear and/or corrosion (lead and copper).
U.S. Pat. No. 2,568,472 discloses a composition containing oil and an amine salt of an acid compound and a hydroxycarboxylic acid, wherein the carboxylic acid group is separated by no more than two carbon atoms and the amine salt is present from 0.01 percent by weight to the limit of its solubility in oil. For example glycolic acid is reacted with water, boric acid, and cyclohexylamine.
A variety of patent publications such as CA 1 183 125, U.S. Pat. No. 5,387,351, U.S. 2005/0198894, U.S. Pat. Nos. 4,640,787, 4,692,257, 4,478,604, 4,237,022, GB 2 105 743, U.S. Pat. Nos. 2,443,578, 2,365,291, 5,338,470, WO 2005/087904, WO 2008/147700, WO 2008/147704, and WO 2008/144701 disclose different lubricating compositions containing hydroxycarboxylic acid amides, imides and esters as antiwear agents. None of these references disclose amine salts of hydroxycarboxylic acids.
International publications WO 2010/096167, WO 2010/096168, and WO 2010/096169 disclose method of reducing wear or friction, and deposit formation and oxidation respectively. The compositions disclosed in the three international publications include a lubricating composition containing base oil, at least one additive selected from anti-oxidant, dispersant, detergent ort anti-wear agent. None of these references disclose amine salts of hydroxycarboxylic acids.
For driveline power transmitting devices such as gears or transmissions, especially axle fluids and manual transmission fluids (MTFs), there are highly challenging technological problems and solutions for satisfying the multiple and often conflicting lubricating requirements, whilst providing durability and cleanliness. One of the important parameters influencing durability is the effectiveness of phosphorus antiwear or extreme pressure additives at providing devices with appropriate protection under various conditions of load and speed. However, many of the phosphorus antiwear or extreme pressure additives contain sulphur. Due to increasing environmental concerns, the presence of sulphur in antiwear or extreme pressure additives is becoming less desirable. In addition, many of the sulphur-containing antiwear or extreme pressure additives evolve sulphur due to numerous volatile sulphur species being present, resulting in lubricating compositions containing antiwear or extreme pressure additives having an odor and possibly also being detrimental to health and the environment.
A lubricating composition having the correct balance of phosphorus antiwear or extreme pressure additives provides driveline power transmitting devices with prolonged life and efficiency with controlled deposit formation and oxidation stability. However, many of the antiwear or extreme pressure additives employed have limited oxidative stability, form deposits or increase corrosion. In addition, many phosphorus antiwear or extreme pressure additives typically also contain sulphur, which results in a lubricating composition containing the phosphorus antiwear or extreme pressure additives are odorous.